At the present time the most widely used process for purifying waste water from coke ovens consists of firstly removing volatile mineral compounds (NH.sub.3, HCN, H.sub.2 S, CO.sub.2) and a small fraction of phenolic compounds by distillation or by entrainment in live steam (stripping), with simultaneous treatment with lime or soda to release ammonia from fixed salts. The water is subsequently freed of the residual phenols and non-volatile compounds by biologocal oxidation in aeration tanks. The ammoniacal vapor is either decomposed in suitable incinerators with the controlled formation of nitrogen oxides, or treated with sulfuric acid to produce ammonium sulfate.
The desorption operation is of notable importance in the purification cycle for the waste water from coke ovens. Any deficiency in this operation leads in particular to the following well-known drawbacks:
(A) OVERLOADING OF THE BIOLOGICAL TANKS, WHERE CERTAIN INHIBITION EFFECTS COULD UNDERMINE THE EFFECTIVENESS OF THE PROCESS;
(B) THE NEED FOR ADDITIONAL FINISHING TREATMENT BEFORE DISCHARGING THE WATER INTO THE NATURAL ENVIRONMENT (FOR EXAMPLE TREATMENT BY ACTIVATED CARBON);
(C) THE RISK OF ATMOSPHERIC POLLUTION ABOVE THE AERATION TANKS BY ENTRAINMENT OF RESIDUAL VOLATILE MATTER.
It is apparent that the desorption operation, whether carried out by distillation or by stripping, must be proceeded with until practically complete if it is to be considered as completely effective. To this end, a process has already been proposed in which a stripping column is used containing substantially horizontal perforated plates disposed one above the other, the top of the column being fed with the waste water to be purified, the bottom of the column being fed with live steam and the column being fed laterally with a strong base at one or more levels. By means of this process, the ammonium salts, whether volatile or not, are removed nearly completely from the waste water, while the other compounds such as phenols are removed from the water by a biological oxidation process.